Patent GB-706744-A (GB)
Title: Improvements relating to train or vehicle describers
IPC: B61L25/04
Filed: 1952-02-29
Abstract: 706,744. Automatic train-describer apparatus; operating railway points. WESTINGHOUSE AIR BRAKE CO. Feb. 29, 1952 [March 3, 1951], Classes 104 (1) and 105 Track apparatus for identifying trains and/or for setting points for a train as it approaches a junction point comprises at a point on the track a transmitting element fed with A.C. at one or more frequencies and a receiving element normally inoperative but rendered operative by electromagnetic or electrostatic coupling to the transmitting element by the passage of a traincarried element tuned to the frequency or frequencies characteristic of the train identity. Preferably the normal coupling between the transmitter and receiver is reduced as low as possible as by suitably locating these items or by neutralizing voltages introduced at appropriate points in the apparatus or by appropriate spacing of the said items. The transmitter may be fed by a plurality of different frequency oscillators or by an oscillator having, e.g. a square wave-form output or by a frequency sweep oscillator. The receiver is coupled to a plurality of tuned amplifiers the outputs of each of which is applied to trigger a respective gas or ionization tube so that the conduction current operates a relay in the anode circuit to control a circuit which governs signal devices at the wayside station or points-operating devices which will set the points in accordance with the destination of the train. To eliminate operation of the receiver amplifiers by coupling between the transmitter and receiver effected by large metallic objects such as the metal sides and floor of a passing carriage by the eddy currents induced therein the phase of the output-voltage of the receiver or tuned amplifier is compared with the phase of the input voltage to the transmitter to detect direction of phase shift and if resulting from the metal object the gas tube is prevented from triggering on application of the output voltage from the tuned amplifier. The transmitter and receiver in the form of inductance coils may be placed on opposite sides of the track and coupled by coils on both sides of the train connected in a tuned circuit. Alternatively metal plates attached to the train act as plates of a condenser to couple corresponding plates located along the track way which are coupled to an oscillator and a tuned amplifier respectively. As shown the transmitter coil TC and receiver coil RC are on the same side of the track 1a 1b. The train carries a coil VC tuned by capacitors 46 or 48 to frequencies 70 Kc. or 50 Kc. being the frequencies respectively of oscillators OSC1, OSC2 feeding the coil TC through parallel-connected secondary windings S1, S3 of transformers T1, T2. The apparatus associated with the respective frequencies are similar and are fed in parallel from the coil RC. The apparatus for the 70 Kc. frequency comprises a tuned amplifier TAM1, fed from coil RC, a discriminator circuit . including a second secondary coil S2 of transformer T1 with a phase-shifting network comprising series-connected resistor 80 and capacity 83 for applying an adjustable-phase reference voltage to the discriminator, a gas tube GT1 and a relay R1 in its anode circuit. The electron tube amplifier TAM1 has tuned input and output circuits to respond only to 70 Kc. frequency and amplifier TAM2 responds only to 50 Kc. frequency. The output of amplifier TAM1 is applied from an output resistor 68 to the centre-tap 64 of the secondary winding 66 of the discrimdnator transformer T7 whose terminals are connected via half-wave rectifying elements Kl, K2 across a pair of resistors 70, 72 with their mid-point grounded. The primary winding 60 of transformer T7 is connected to the centre-tap of the secondary winding S2 of transformer T1 and a variable tap on resistor 80. The gas-tube GT1 is normally biased to a non-conductive condition as by connecting the cathode 25 through resistor 26 to the junction of the potentiometer resistors 27, 28 connected across a battery supply, the low potential end of resistor 28 being grounded. The anode circuit of tube GT1 is from battery positive terminal B over front contact 29 of track relay TR, wire 30. normally closed push button 31, wire 32, winding of relay Rl anode 33 to cathode 25, resistors 26. 28 to ground. The phase of the A.C. current in the secondary winding of transformer T7 is adjusted in phase with the output of amplifier TAM1 when a traincarried coil couples the coils TC and RC. Positive half cycles of rectified A.C. reference voltage supplied through transformer T7 and rectifiers Kl, K2 aided by the in-phase output of the other amplifier TAM1, build up a positive potential on capacity 76 and this potential is applied to drive the grid 24 of gas tube GT1, sufficiently positive with respect to its cathode to fire the tube causing relay Rl to pick up and at front contact 42 close the circuit for the indication lamp D1. e.g. of a train indicator, In like manner lamp D2 is lit on recepton of 50 Kc. frequency. In the presence of a metal object coupling coils TC and RC the output from amplifier TAM1 is out of phase with the A.C. reference current in the secondary winding 66 and the rectified voltage is insufficient to fire the tube GT1. On the train leaving the station ST the track relay TR is dropped and at its contact 29 interrupts the anode circuit of the gas tube GT1 and the energizing circuit of relay Rl to restore the tube to its non-conductive condutian and to extinguish lamp D1. This restoration may also be effected by the pushbutton 31. Various dispositions of the coils RC and TC are described.